In recent years, in order to efficiently use an air conditioner for environmental pollution measures and power saving, a need for limitation of the air in a room has increased. For example, in order to prevent allergens such as toxic gas contained in the outside air, dust contained in an exhaust gas of an automobile and the like, fine particulate matters (PM 2.5), and pollen from entering a room, a need for ventilation and circulation of the air in the room has increased. In addition, in a case where a temperature in the room is adjusted by the air conditioner or the like, in order to save power consumption, it is desired that the ventilation is performed by using (circulating) the air in the room instead of using the outside air as it is.
On the other hand, human beings inhale oxygen in the air by respiration, and exhale exhalation gas containing a large amount of carbon dioxide. In a case where the volume of an enclosed space is small (that is, the space is narrow), and a density of people present in the enclosed space is high, a carbon dioxide concentration in the space is increased. However, the carbon dioxide is a colorless and odorless gas, and thus it is difficult to recognize that the concentration of the carbon dioxide is increased. Therefore, it is important to properly control the carbon dioxide concentration.
Regarding a state where the carbon dioxide concentration in the space is rapidly increased when the above-described ventilation limiting of the enclosed space is performed by using the air in the enclosed space, an example of a change of the carbon dioxide concentration over time in a case where one adult and two children are present in a compartment of an automobile is illustrated in FIG. 11. FIG. 11 is a graph illustrating an example of a result obtained by measuring the change of the carbon dioxide concentration in a compartment of a vehicle over time in a case where total three people of one adult and two children ride in a compartment of a light-weight vehicle (a light-weight wagon). In a case where the ventilation is performed through the air from the outside of the compartment by opening a window (graph P2), even after the lapse of 20 minutes, the carbon dioxide concentration in the compartment is approximately 500 ppm, and an increase in the carbon dioxide concentration was not found. On the other hand, in a case where only the air in the compartment was circulated by closing windows and doors (graph P1), the level of the carbon dioxide concentration in the compartment exceeded 1000 ppm in five minutes, and approached up to 5000 ppm in 50 minutes. A carbon dioxide concentration C2 at 1000 ppm is a concentration (an upper limit value regulated in Buildings and Health Act) which has been known for a bad influence on a human body such as loss of concentration and inducement of sleepiness. In addition, a carbon dioxide concentration C1 at 5000 ppm is a concentration set as an allowable concentration (a recommendation value of the Japan Society for Occupational Health) of the chemical Material Safety Data Sheet (MSDS).
As such, it has been known that in the enclosed space such as the inside of the compartment of the vehicle, the carbon dioxide concentration in the space is rapidly increased. For example, PTL 1 discloses an air conditioning system for a vehicle in which a selective separating material having a function for permeating oxygen and carbon dioxide in a space, and shielding hydrocarbon, nitrogen oxide, sulfur oxide, and microsolid components is arranged so as to separate the inside from the outside of the compartment of the vehicle.